Potassium channel subunits containing two pore domains (“K 2P channels”) form a novel class of background K+ channels. These K 2P channels have unique pharmacological and functional properties (1-10). They are active at all membrane potentials and display very rapid kinetics of activation and deactivation, and no inactivation. Their widespread tissue distribution suggests that one of their major physiological roles is setting the resting membrane potential in many different cell types. Background K+ channels with specific functional and regulatory properties, as well as unique tissue distribution, have now been cloned. These channels could be involved in more specific functions such as epithelial K+ transport and regulation of neuronal and muscular excitability (11).
Various K+ currents have been recorded in vivo from neuronal, cardiac and smooth muscle cells, that form a subfamily of background K+ currents sensitive to fatty acids (12-15). Recently, fatty acid-activated K+ channels have been cloned from mice and humans (2, 6, 16). These channels named TREK1 (TWIK-Related K+ channel) and TRAAK (TWIK-Related Arachidonic Acid-stimulated K+ channel) produce quasi-instantaneous currents that are outwardly rectifying in physiological K+ gradient. These channels have a low basal activity compared to TASK background channels (3-5). However, they can be strongly activated by application of arachidonic acid. This effect is specific for unsaturated fatty acids.
Oleate, linoleate, eicosapentaenoate and docosahexaenoate all strongly activate TREK1 and TRAAK, while saturated fatty acids such as palmitate, stearate and arachidate are ineffective (6, 17). Another efficient way for activating these channels is the application of a stretch to the cell membrane (17, 18). Both channels are activated by shear stress, cell swelling and negative pressure. They are mechano-sensitive K+ channels.
Compared to TRAAK, TREK1 has additional features. TREK1 is inhibited by activators of protein kinases C and A (PKC, PKA). The site for PKA phosphorylation has been localized in the cytoplasmic carboxy-terminal part of the channel (17). TREK1 but not TRAAK is opened by internal acidification (19). Lowering pHi shifts the pressure-activation relationships toward positive values and leads to channel opening at atmospheric pressure. TREK1, but not TRAAK, is activated by inhalational general anesthetics, halothane and isoflurane, at concentrations used in human general anesthesia (16). Finally, TREK1 and TRAAK have different tissue distributions, the expression of TRAAK being more restricted to neuronal cells than TREK1 (2, 6, 20).
This invention describes the cloning, the genomic organization, the localization and the functional characterization of a novel human K+ channel with two pore domains. The molecular and functional properties of this channel indicate that it too belongs to the particular subclass of mechano-sensitive and unsaturated fatty acid-activated K+ channels. TREK2 is more related to TREK1 than to TRAAK, and like TREK1, it is activated by general anesthetics at clinical concentrations. Moreover, TREK2 is modulated by different types of neurotransmitter receptors. In high symmetrical K+ conditions, TREK2 produces currents whose current-voltage relationship is weakly inwardly rectifying.